Filter unit



FIG. 1 is a perspective view of a filter unit of my new appearance design as it appears in operation suspended from overhead and with filter media in place;

FIG. 2 is an additional perspective view of the filter unit of FIG. 1 showing the bottom, rear and opposite sides not visible in FIG. 1; and

FIG. 3 is a perspective view from the same orientation as FIG. 1, but showing the appearance of the filter unit with the filter media and rolls removed. 

The ornamental design for a filter unit, as shown. 